Improving the efficiency of our nation’s buildings certainly isn’t a new goal. The energy crisis of the 1970s spurred a wave of energy-reducing innovations, including the first generation of building-mounted photovoltaic (PV) panels to produce electricity on-site. Since then, the U.S. Green Building Council began its charge on reducing building energy use with its Leadership in Energy and Environmental Design (LEED) certification program, launched in 2000. More recently, though, the idea of essentially eliminating a building’s annual energy impact has taken hold, with existing buildings now seen as viable targets for such significant energy-efficiency improvements.


It does seem almost impossible that a building could consume only as much energy as it generates on its own, over the course of a year. But the dream of such “net-zero” performance has become a reality in a number of signature U.S. projects in the past few years. Though it is primarily a target for new construction, net-zero now also is being considered when existing buildings are ripe for major renovation. In many cases, it is simply not achievable. However, in exploring the possibility, building teams are reducing energy use far below what once was thought possible.


Net-zero buildings are still connected to the local electricity distribution grid because there will be times when they are net consumers of electricity—such as during a northern winter, when early sunsets mean natural daylight starts disappearing by early afternoon. At other times, though, such as during a sunny summer afternoon, roof-mounted PV panels may make the buildings net producers. For this reason, the net-zero appellation is earned through an averaging of energy consumption and production over a 12-month period.


The tower of power


Improving the efficiency of existing structures has been a goal for some time, but most upgrades have focused on single systems with easy paybacks, like lighting or ventilation-system motors. Recently, groups such as the Rocky Mountain Institute (RMI), Snowmass, Colo., have begun championing the idea of “deep” energy retrofits, which are efficiency-­improving initiatives looking more holistically at an entire building’s performance. 


The Empire State Building’s 2010 overhaul has become a signature success story of this movement. The efficiency improvements were enacted alongside a $550 million update to finishes and systems that were designed to reposition the building as Class A office space. It is estimated the building will cut annual energy bills by $4.4 million (the tenant space has not been completely built out yet).


RMI was a lead consultant on the Empire State Building’s energy designs. Victor Olgyay, an architect and principal in the organization’s Buildings Practice, said this project used the approach championed by RMI’s approach to deep energy improvements, dubbed RetroFit.


“We usually try starting out with a careful assessment of goals of the owner or operator of the building,” he said. “A lot of times, people don’t even know what might be possible.”


A series of workshops can help building owners understand possibilities and figure out their actual goals. Many owners will be focused on dollars and cents, so net-zero energy costs may be a goal. Environmental groups, or companies seeking to burnish their green reputations, may be more interested in net-zero carbon emissions.


“I think the way you define it has a lot to do with the actual goals of the organization,” Olgyay said.


With these goals in mind, software-based energy modeling may start to come into play, especially in larger buildings with complex interactions between systems. 


“You can’t really tell on a spreadsheet that, by upgrading windows, you can downsize the HVAC,” Olgyay said, noting, however, that modeling becomes more expensive as square footage goes down. “With smaller buildings, you usually don’t have as much of a budget, so it becomes more critical that the energy modeling is done effectively.


[SB]The point of the modeling in a net-zero effort is to bring a building’s energy demand down as low as possible, reducing the amount of on-site energy that needs to be generated. Where on-site generation isn’t feasible—as in a project such as the Empire State Building—the modeling can reduce the amount of renewable energy a company might want to purchase to establish itself as net-zero in terms of carbon impact.


Several additional project launches, including the Byron Rogers Federal Building in Denver, have followed the Empire State Building’s success. Some may have seen the 1965 high-rise, with its failing curtain wall and aging mechanical systems, as a good candidate for outright replacement. But as a signature example of mid-century governmental architecture, the building will be eligible for listing on the National Register of Historic Places in 2015. Plus, the adjacent courthouse—originally designed in tandem with the office building—was renovated in 2005.


Tim Gaidis is a sustainability expert with HOK, the St. Louis-based architecture firm overseeing the renovation effort, which has become a gut-rehab project. Contractors are essentially creating a new building in the existing shell, in an effort that includes installing all new windows and replacing the existing forced-air mechanical equipment with a much more efficient chilled-beam hydronic system.


Even with such options, though, the design team had several strikes against its net-zero goals before it even sat down to its electronic drawing boards. First and foremost, the building is sited at 45 degrees on the compass; in contrast, a new net-zero structure would more likely be sited with its long axis running east to west, so light could be maximized for natural illumination. Additionally, because the U.S. Government Services Administration (GSA), the building’s owner, will be seeking historic status, any exterior improvements had to remain visually true to the original appearance—so window tinting or sunshade devices were out of the question.


Turnover to net-zero


However, as the owner and operator of most federal real estate, the GSA is under a mandate issued in an executive order by President Obama in 2009 to bring all new federal buildings to net-zero status by 2030. Additionally, federal agencies that become the building’s tenants are under the same 2030 deadline in any space they lease—from the GSA or any other landlord.


“We realized that with this executive order, that all of these 10 agencies were going to have to meet the 2030 challenge, so we proposed a path-to-net-zero plan,” Gaidis said. “Many of those strategies aren’t in the project budget at this time.”


Net-zero goals, along with deep energy retrofits, also are being applied to existing homes—an effort in which Bill Zoeller, a senior vice president with the Norwalk, Conn.-based Steven Winter Associates architecture firm, is deeply involved. The firm is heading up the Consortium for Advanced Residential Building (CARB) research team for the U.S. Department of Energy’s Building America program; Zoeller is leading the project.


Zoeller noted the difficulties in achieving true net-zero performance with existing home upgrades.


“You’re obviously limited by the existing configuration and thicknesses of walls,” he said, adding that his team had successfully met these challenges in a Las Vegas demonstration project. Through a variety of improvements to insulation, windows, lighting and appliances, this home’s original annual energy consumption of 30,000 kilowatt-hours (kWh) was cut to an estimated 9,000 kWh. To offset this demand, a 6-kilowatt PV panel system was installed on the roof.


Admittedly, Las Vegas’ low humidity makes cooling and insulation issues easier to address than they might be in other regions, as a similar attempt to reach net-zero performance in Florida proved. However, even in this high-humidity environment, the CARB team reduced total annual energy consumption by 49 percent. This success (which involved no on-site generation to offset demand) begs a question: Is the incremental benefit of true net-zero existing home worth the added expense versus more easily achievable deep energy-retrofit improvements?


To go it alone or spread around the savings?


“If the goal is to take a pre-existing building to zero—with the same effort, we could probably take four buildings to 50 percent,” Zoeller said.


Similarly, HOK’s Gaidis and RMI’s Olgyay noted an emerging trend to spread net-zero targets across groups of buildings instead of expecting each individual structure to hit net-zero.


To explain this concept, Olgyay cited work RMI is doing with Arizona State University in Tempe to develop a roadmap leading to campus-wide net-zero performance by 2025. Like any community, a university campus incorporates a variety of buildings, each offering its own efficiency challenges and potential. An energy-intensive research lab, for example, may never get to net-zero, while an adjacent building might actually be net-zero positive (meaning its rooftop solar panels might actually generate more power than the building consumes). Spreading a limited budget across both buildings could bring an average of net-zero performance at a much more affordable cost.


Olgyay sees this move to view buildings as part of broader systems as a next step toward a larger goal, “to start thinking about this network of community,” he said, noting the mounting fears the increased use of distributed generation (such as rooftop PV panels) could impact electric utility operations. 


“The grid is starting to feel those pressures, anyway,” Olgyay said.